The Yeerk Invasion of Hogwarts
by Shiny Snicket
Summary: Albus Dumbledore notices something strange about the new Defence Against the Dark Arts teacher, Professor Chapman. The Yeerk invasion spreads to the wizarding world as Hogwarts faces an enemy from beyond the stars.
1. Professor Chapman

**Author's Note: **In this crossover fic, Mr Chapman from _'Animorphs'_ is a wizard and he brings the Yeerk invasion to Hogwarts. Apart from Chapman himself and Melissa (who is eleven years old in this) no Animorphs characters will be featured. This is just my idea of what would happen if the Yeerks invaded the magical world as well as the muggle world. It takes place in Harry's third year at Hogwarts, but none of the stuff with the Dementors and Sirius Black is going to happen. Enjoy!

**Disclaimer:** I own neither _'Animorphs'_ nor _'Harry Potter'_.

OoOoO

Professor Albus Dumbledore relaxed in his chair, watching the hungry students become lost in the magnificent feast which was prepared by the house elves of Hogwarts School of Witchcraft and Wizardry. He had a hunch that this year at Hogwarts would prove to be an interesting one. He looked to his right, where the new Defence Against the Dark Arts teacher was taking a sip of pumpkin juice. To most people, Professor Chapman didn't look any different to any other professor. He was a stern person, but certainly not a cruel one. He reminded Dumbledore somewhat of Professor McGonagall in that respect. Dumbledore knew that he would have to keep an eye on Chapman. After all, Dumbledore had a bad history of hiring teachers for this position. The last person to teach Defence Against the Dark Arts at Hogwarts was Gilderoy Lockhart, who turned out to be an arrogant fraud. Lockhart's predecessor was Professor Quirrell, who was possessed by Lord Voldemort. Dumbledore knew that repeating his mistakes wasn't an option.

Professor Chapman previously taught in the Salem Institute of Magic in America. Dumbledore had talked to some of his old colleagues and they only had positive things to say about him. He had a wife as well as a daughter named Melissa. Dumbledore had just watched Melissa get sorted into Hufflepuff. She was very quiet, but otherwise seemed like an ordinary girl. By the time his investigation was over, Dumbledore was convinced that Professor Chapman was a trustworthy man, but that didn't get rid of the nagging sensation at the back on Dumbledore's head. Something about this man was... off. Dumbledore had sensed his magical aura and noticed something strange. He had the magical aura of a reasonably talented wizard, but it was like there was something else there. Something more. When Mr Filch ran up to Dumbledore to discuss some mundane case of students misbehaving, the headmaster of Hogwarts stopped thinking about Chapman. He decided to trust Chapman for the time being, but he also intended to keep an eye on him throughout the school year.

OoOoO

Meanwhile, at the Gryffindor table, three friends were enjoying the first feast of the school year. Harry Potter, Ron Weasley and Hermione Granger were hoping that they would finally get to enjoy a quiet year at Hogwarts. Unfortunately, the three Gryffindors would not get their wish. Ron used his fingers to lift a bacon-wrapped sausage into his mouth, much to Hermione's disgust. Ron started chewing and tried to speak at the same time.

_"Whadyu 'ink 'outda noo 'efence 'eecher?"_ Ron scoffed as tiny pieces of sausage flew out of his mouth.

_"Honestly, Ronald!"_ Hermione scolded, _"Swallow your food before you speak."_

Ron did so then repeated himself, this time much more clearly. _"What do you think about the new __Defence teacher?"_

_"I'm not sure"_, Harry answered hesitantly, looking up at the cold man who was looking around the classroom with a stern look on his face. _"He doesn't look that great to me."_

_"Don't be so suspicious"_, Hermione advised him, _"Professor Dumbledore wouldn't have hired him if he wasn't a competent teacher. I'm sure he'll be fine."_

_"What about Quirrell?"_ Ron blurted out, challenging his friend's logic. _"Same with Lockhart."_

Hermione sighed, taking another sip of her pumpkin juice. _"People learn from their mistakes, Ronald." _

Before Ron could respond, Professor Dumbledore stood up and announced that the feast was over. He ordered the students to go to their respective common rooms. The prefects rushed over to the new first years to show them where to go, while Harry, Ron and Hermione stood up and quickly walked away. Dumbledore kept his gaze fixed on Melissa Chapman, trying to figure her out. She had the magical aura of an ordinary eleven-year-old girl and unlike her father, there wasn't _'something else'_ in her aura. She seemed perfectly ordinary. Dumbledore's concentration was broken when he was approached by Professor McGonagall, who wanted to ask him about the timetables which she was preparing for her students. Dumbledore nodded at everything the transfiguration teacher said, not really listening at all. His mind was still preoccupied with the task of figuring out who Chapman really was.

OoOoO

Professor Hedrick Chapman retired to his quarters early, keen to give the good news to the visser. His first day in Hogwarts went according to plan and nobody seemed to notice anything odd about him. None of the students or faculty would have ever guessed that he was being controlled by a slug-like alien creature called a Yeerk. The Yeerk was one of the foulest creatures in the known universe. They were parasites who live off hosts, such as human beings. The Yeerks crawl into the ear of their hosts. They enter the brain via the ear canal and take over their hosts' body. The host no longer has any control of what they do or say. They have lost all of their freedom. When someone loses their freedom to a Yeerk, they become what is known as a Controller. Professor Chapman was the first Controller to ever to make it into Hogwarts grounds.

He took out a quill and a piece of parchment and began to write to Visser Three, the Yeerk who was in charge of the invasion of Earth. The invasion had already proved successful in the muggle world, but this was the first time that the Yeerks took a step into the wizarding world. Chapman was honoured that Visser Three trusted him with such an important job. However, he was also afraid for his life. He knew that the visser did not tolerate failure. If Chapman were to fail, he would be killed by Visser Three or worse, left to die of Kandrona starvation. The Yeerk needed Kandrona particles in order to survive. The Yeerk planet's sun generated these particles, but Earth's sun did not. The only other means by which a Yeerk can absorb the Kandrona particles is for it to submurge itself into a Yeerk Pool, which is a body of water which contains Kandrona rays. Chapman knew that he would not be able to survive even three days without finding a way to build a Yeerk pool somewhere that is easily accessible for those attending Hogwarts. It was imperative if he wanted to begin infesting students.

Professor Chapman knew that Visser Three would only want a brief report, one that is short and to the point. The visser was a very impatient Yeerk, who did not like it when others wasted his time. Knowing how terrifying Visser Three could be, Chapman knew that he had to be cautious.

_Visser,_

_Please excuse me for using human means of communications to send this update to you. It is simply the most convenient course of action. The bird that brought this letter is called an owl. There is no need to shoot it as I have made sure that it is not one of the Andalite bandits in morph. To the point, I am inside Hogwarts School of Witchcraft and Wizardry and have successfully fooled the humans. I would like to thank you again for trusting me with such an important job. The wizards and witches of planet Earth will fall, just like the rest of the humans. I await your orders._

_Iniss 226_

Professor Chapman signed the letter with his Yeerk's name, before walking to the owlery and sending the letter. He really had no way of knowing that the owl wasn't an Andalite, but he wanted to give Visser Three peace of mind. There was no way that the Andalites could have already found out that the Yeerks planned to invade the wizarding world. Chapman smirked smugly to himself. Hogwarts was defended by so many wards, defences so much more effective than what the rest of the pathetic human race could ever come up with. Yet Chapman simply walked into the school and the staff let him in. The plan was working to perfection.

The Yeerk invasion of Hogwarts had officially begun.


	2. The Yeerk Pool

**Author's Note: **I wasn't really expecting any reviews since this is a very niche story that appeals to a tiny fraction of the people on this site. This is something I'm just going to update from time to time for fun, but I hope that at least a couple of people are reading this.

**Disclaimer:** I own neither _'Animorphs'_ nor _'Harry Potter'_.

OoOoO

The students of Hogwarts were noisily chatting and enjoying their breakfasts. Professor Chapman sat at the staff table and was just about to take a bite out of his toast when he noticed something odd about one of his colleagues. Severus Snape, the potions master at Hogwarts, was looking at Chapman with a suspicious look in his eye. Chapman paled slightly, wondering if Snape might have figured out that Chapman wasn't exactly in control of himself right now. Eventually, Snape turned away from Chapman and stood up. He quickly walked out of the Great Hall, most likely going down to the dungeons to prepare for the morning's potions classes.

Chapman dismissed the idea that Snape might be suspicious. From what the new professor had seen, Snape had that evil look in his eyes all the time. It wasn't a sign that he knew about Chapman. After all, how could Snape, a mere human, know about the Yeerk invasion of Earth? If a new teacher started acting strangely, would Snape seriously come to the conclusion that he had a slug-like parasite inside his head? That was ridiculous. Snape didn't even know the real Hedrick Chapman. They had never met when Chapman was in control of his voice or his body. The Yeerk inside Chapman's head knew that the human race was always reluctant to believe in something they don't understand. That would be their downfall.

At that moment, Chapman turned his attention to Professor Dumbledore, who stood up and waited for the murmurs of the students to fade. Eventually, silence filled the Great Hall as they waited to fund out what Dumbledore had to say. Chapman know that everyone always put blind faith in that delusional, old man. Chapman was going to use that. He had discussed the formation of a new group, the Sharing, with Dumbledore the day before the students arrived. If Dumbledore advertised it, the turnout would double. So many hosts would just walking into the slaughter house, although the would have to come to terms with a fate much worse than death. Albeit unwittingly, Dumbledore was about to condemn the entire wizarding world to slavery.

"_Before you go to your first class of the school year, I have an announcement to make. I neglected to mention this last night at the welcoming feast, so please be attentive."_ Dumbledore paused as Chapman smirked. Here it comes.

"_There will be a new group forming at Hogwarts this year, aptly titled the Sharing. Whoever joins this group will be able to take part in various activities throughout the school year. You will learn admirable virtues and ideal values. I am also assured that the activities will be a lot of fun. Any student wishing to join will simply have to give their names to the new Defence Against the Dark Arts teacher, Professor Chapman. With that said, it's time to take the first step into what I hope will be a very productive year of class." _Dumbledore cleared his throat after finishing his speech.

While he walked out of the Great Hall, Chapman struggled to control the urge to grin widely. He couldn't wait to send an owl to Visser Three, telling him the good news. Soon, he would have the entire student population in the palm of his hand... or in the palm of his host's hand, at least. Now he only had the problem of finding a Yeerk Pool inside the castle itself.

OoOoO

Harry sat down between Ron and Hermione as he prepared for his first Defence Against the Dark Arts class of the year. He looked up at Professor Chapman, hoping that the new professor would prove to be competent.

"_I wouldn't get your hopes up," _whispered Ron, as if he were reading Harry's mind. _"I don't think he's going to be any better than Quirrell or Lockhart. Did you hear what Dumbledore said about that Sharing thing? Sounds to me like a gathering of the new defence teacher's favourite pets."_

"_Ron!" _scolded Hermione. _"The Sharing sounds like a wonderful way to make new friends and learn new thing. I hope it doesn't get in the way of homework and studying though. I was thinking of joining."_

"_Of course you were." _Ron let out the words as he chuckled, as if Hermione had done nothing but prove his point.

Chapman took that moment to address his third year class for the first time.

"_Welcome, third years. Put your books away and take your wands out. I think it would be best if we start with a practical lesson."_ He said calmly.

Everyone in the class was happy to hear this news, with the sole exception on Hermione Granger. They took out their wands excitedly. Chapman, despite being extra-terrestrial, knew enough about the human understanding of magic to teach a class. After all, the real Chapman had taught in the Salem Institute of Magic. Whatever the host knows, the Yeerk knows. Whatever is in the human's mind is equally in the Yeerk's. Chapman was determined to be a competent teacher in order to avoid suspicion from Dumbledore and the others. He had a surprise in store for this class.

"_We are going to be covering dark creatures and how one can defend oneself against them" _He said as he dragged a large box into the middle of the room. _"The first creature you will learn to defend yourself against is in here."_

The class looked closely at the box, wondering what could possibly be inside.

"_Who can tell me what fear looks like?" _said Chapman after several moments of stalling.

There was silence.

"_Like this," _the new professor whispered softly as he opened the box and released the boggart inside.

It was at this moment that Chapman realised him mistake. He had been so busy thinking of a way to bring a Yeerk Pool to Hogwarts recently that he didn't think it through. He had just assumed that the boggart would have taken the form of the real Chapman's worst fear. However, since the Yeerk inside held the dominant position in the mind, the boggart transformed to take the shape of Iniss 226's worst fear.

It was a terrifying creature known as an Antarean Bogg. This huge, fearsome species was genetically engineered by the Arn. It was one of the morphs that Visser Three had access to in his Andalite host body. The visser used this morph to devour the Andaline known as Prince Elfangor-Sirinial-Shamtul. There was nothing that the Yeerk feared more than the punishment that Visser Three would give him if he failed. That's why he had no choice but to ensure the infestation of the wizarding world.

His hand trembling, Chapman raised his wand and let out the incantation, _"Riddikulus!"_

Suddenly, Visser Three shrank and involuntarily morphed back into his true host form. The Andalite looked around, not sure what was going on. Then, all of a sudden, the Andalite's tail blade turned on his, attacking him with several slashes, scarcely missing the visser's neck. The class watched in both confusion and wonder as Visser Three stumbled back into the box.

Chapman almost found himself cursing aloud. The students had all seen two alien races that humanity should know nothing about, an Antarean Bogg and an Andalite. That was bound to make someone suspicious. Chapman decided to immediately let the students tackle the boggart themselves. Maybe the anxiety of having to face a boggart would be enough to distract them from what they had seen.

"_When I open this box again," _Chapman began, _"It will take the shape of whatever the observer fears most of all. The way to defeat a boggart is to use the Riddikulus charm. Simply point your wand at the boggart, say the incantation and imagine your fear turning into something which funny. Enough chat, let's begin!"_

Chapman opened the box again and the boggart was freed. Chapman watched Dean Thomas turn his worst fear, a disembodied hand, into something amusing by catching it in a mouse trap. He watched Parvati Patil make a mummy trip on its own bandages. He watched Hermione Granger defeat the boggart when it transformed into Professor McGonagall. Seamus Finnigan made a banshee lose its voice and Ron Weasley made a giant spider lose its legs. The last student in the long line was Harry James Potter.

Chapman watched with interest as Harry approached the boggart. Ron gave him a few words of reassurance as Harry slowly took a few steps towards it. His shoes made the floorboards creek as Chapman leaned forward to get a better view. He know through his host that Harry was a living legend, the Boy-Who-Lived. Chapman knew that he had to keep an eye on this one, or even better, infest him. Wouldn't it be a stroke of look if Harry turned up at the Sharing?

The boggart was just about to change form, when Chapman looked at his watch. He realised that he was supposed to let the students out to their next class five minutes ago. He quickly closed the box, sealing the boggart inside it.

"_My apologies," _started Chapman, _"I've made you late for your Charms class. Please extend my apoligies to Professor Flitwick. Now go before I get it trouble."_

The students left the classroom chatting about their individual experiences with the boggart. Chapman noticed that Harry look glum made his way out of the room. He stopped him.

"_If you're disappointing about not getting a chance to face the boggart," _the teacher said to him, _"you can come to the first meeting of the Sharing. We can do it there. I'll bring the boggart with me just in case you decide to come."_

"_Thank you sir," _mumbled Harry with a hesitant nod.

Chapman watched as Harry left the classroom and hurried after his friends. He took one last look at the Boy-Who-Lived for the time being, before silently praying. _Please let him come to the Sharing._

OoOoO

After class ended, Chapman made his way towards the Hufflepuff dormitories in search of his daughter, or his host's daughter, Melissa Chapman. He wanted to check how her first day of class went. She seemed very quiet when her father had he for Defence Against the Dark Arts class. On his way he couldn't stop thinking about his dilemma. He arrived at the school a day before the students. It had been two days already. He was already beginning to feel the pain of Kandrona starvation. He had one more day to figure out how to somehow bring a Yeerk Pool to Hogwarts without Dumbledore finding out. Otherwise, he would die painfully.

Chapman thought about this problem as he wandered across the seventh floor of the castle. He looked over at the tapestry of Barnabus the Barmy. He cursed under his breath. He was sure that he had already passed this tapestry twice. Hogwarts was like a maze. The human architects who designed it must have purposely decided to torture anyone who wanted to walk the halls without the company of someone who knew the castle well. Chapman heard a strange noise, so he looked to the side to see a door suddenly appearing out of thin air in the wall opposite the tapestry.

A curious Professor Chapman opened the door and walked through. He was overwhelmed by the sudden realisation that his problem had been resolved. The real Chapman had heard legends about the Room of Requirement. After all, his parents considered sending him to Hogwarts when he was young. However, they eventually decided that it would be better if he stayed in America. Chapman was delighted to discover that the room was equipped to the seeker's needs as it always was.

Chapman found himself staring at the one thing he needed most.

A gigantic Yeerk pool, surrounded by cages for holding prisoners.

Good news for Chapman. Bad news for humanity.


End file.
